Optical detectors now in use are based either upon the detection of the interruption of the light beam emitted by a light source as an object passes therethrough or upon the detection of the light beam emitted by a light source and reflected to a receiver by a passing object. In detectors of the first-mentioned type, the source and the receiver are disposed opposite one another across the path of the moving objects; in detectors of the second type, the source and the receiver are disposed side by side on the same side of the path followed by the moving objects.
In many optical detectors, the light source is associated with electronic control circuits enabling the light from the source to be differentiated from the ambient light.
Such circuits may comprise an oscillator with a constant cycle ratio and a fixed oscillating frequency on the order of 20 kilo-Hertz, piloting a power stage controlling a visible light emitting diode serving as the light source.
In a similar way, the receiver, consisting of a photodiode, is associated with electronic circuits for processing the received signal, said processing involving signal detection and comparison of the signal with a fixed or variable reference signal. The latter electronics may include a current-to-voltage converter of the signal from the light-receiving photodiode, followed by a power amplifier, a High-pass type filter of the amplified signal, an integrator-type detector to detect a change in signal level resulting from the passage of an object to be detected, a comparator and a signal output stage.
These diode control and signal processing electronics may advantageously be combined with the diode and the photodiode into a single package with optical conduits going therethrough. These optical conduits are factory-installed at the same time as the electronics and the optical devices. They are secured to the walls of the package which they traverse and given a suitable preset length to provide the required linkup, for the specified operating conditions of the resulting, final detector product, between the package's internal components and the facing or side by side object passage detection points. Such a detector or any similar detectors used in an automatic machine are powered through electric cable; their electric signal output is transmitted along a dedicated electric cable to a processing circuit mounted on a printed circuit board, through which automatic control of the machine is enabled. Moreover, the location of such detectors in an automatic machine is determined by the length given said optical conduits.